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As Nokia's cell phone business declined, it started filing patent lawsuits. Nokia was unafraid to sue giant competitors like RIM and Apple. The Finnish company's aggression was one of the key factors that ended the detente between tech companies who used to avoid patent spats for fear it would only lead to "mutually assured destruction."

Microsoft paid billions for a license to Nokia's patents, but the company has made explicit that Nokia still owns the patents. The genius of this move is that it allows Microsoft to double down on its patent war with Android. Microsoft boasts that the majority of Android phones sold worldwide have already paid for a license to Microsoft patents. By 2011, patent licensing revenue exceeded Microsoft's revenue from Windows Phone.

Now, Nokia can go after Android phone makers for royalties—even ones that have already paid Microsoft.

When pressed on the issue today, a Nokia spokesman confirmed that more patent licensing is indeed part of the plan.

"Once we no longer have our own mobile devices business, following the close of the (Microsoft) transaction, we would be able to explore licensing some of those technologies," a company spokesman told Reuters.

IP experts who spoke to Reuters said that Nokia's unusual decision to not sell the patents along with the business means that it has other plans for recouping value from those patents. While Nokia is not a "patent troll" because it will continue to have an operating business, it is effectively embracing a similar strategy. The combination of a powerful patent portfolio and no operating phone business to counter-sue will make Nokia a formidable opponent in court.